1. Field of the Invention
This invention relates generally to heat exchangers, and in particular to a forced air heat exchanger for use with a fireplace, wherein the heat exchanger forces room air through a heat reservoir located within the fireplace and recirculates heated air back into the room.
2. Description of the Prior Art
It is common for fireplaces to adorn rooms for aesthetic purposes, but it is even more common for fireplaces to be used as a means for heating those rooms. With the escalation of energy costs over the past two decades, many homeowners now rely upon fireplaces to augment their existing heating capabilities. While fireplaces do effectively contribute to the heating of homes and other buildings, it has long been known that they lose some heat though their chimneys. Also, the heat generated by the fire is not efficiently distributed throughout the room or rooms to be heated. Consequently, various heat exchangers have been developed to increase the heating efficiency of fireplaces.
Many contemporary fireplaces include a decorative frame insertable within the front of the fireplace. A set of glass doors, or a metal mesh curtain are often housed within the frame to prevent hot ashes from escaping the fireplaces. The glass doors also provide an aesthetic appeal to the fireplace. Further, when the glass doors are closed the rate of fireplaces burning can be better controlled. Thus, it may be advantageous to provide a fireplace heat exchanger that is compatible with closed glass doors.
One heat exchanger is disclosed in U.S. Pat. No. 4,074,681, issued to Whiteley on Feb. 21, 1978, that includes a U-shaped conduit placed flat on the floor of a fireplace and a fan that forces air from a room through the conduit. The inlet of the conduit is disposed on the opposite side of the fireplace as the outlet of the conduit. The heated air is subsequently exhausted back into the room. The center portion of the U-shaped conduit rests on the floor of the fireplace and the material to be burned is placed at least partially on top of the center portion. Thus, the center portion must be constructed of material capable of withstanding constant exposure to the hottest part of the fire, which increases the cost of construction. Also, prolonged exposure to such intense heat may cause the material to degenerate leading to possible repair or replacement.
Another heat exchanger is disclosed in U.S. Pat. No. 3,955,553, issued to Soeffker on May 11, 1976, that includes a forced air blower to provide a pressurized air flow through a plurality of laterally spaced tubes positioned within a fireplace. A manifold is connected to the blower that directs air into the tubes. The manifold is removable so that air can alternatively flow through the tubes by conversion. The heated air subsequently flows back into the room. The configuration of this heat exchanger does not lend itself for use with fireplaces having a frame, or a frame that houses glass doors. In particular, it would not be practically possible to use this heat exchanger with the glass doors closed.
U.S. Pat. No. 3,880,141, issued to Abshear on Apr. 29, 1975, discloses a heating system for fireplaces that positions a relatively flat heat exchanger at the rear of a fireplace. An air inlet duct is connected to the lower end of the heat exchanger and a hot air outlet duct is connected to the upper end. An electric pump or fan blows air from a room through the inlet duct, through the heat exchanger, through the hot air outlet duct, and back into the room. The cabinet and duct work of this heating system are rather cumbersome and not readily adaptable for use with contemporary fireplaces that typically include closable glass doors, or wire mesh curtains.
A previous design developed by the applicants includes an elongated manifold into which room air is initially forced by a variable speed motor. The manifold rests upon the hearth extension and acts as a conduit through which the air is forced. It is connected to the motor by a funnel shaped conduit. As air flows from the motor through the manifold, some of the air flows into an input conduit while some air is forced past the input conduit toward the center of the manifold. A block is located within and near the center of the manifold to prevent air from being forced through the length of the manifold. When air contacts the block it is redirected toward the input conduit so the air can flow through the input conduit and consequently a heat reservoir, in which the air is heated.
An extension segment is connected between the input conduit and a first riser tube that leads to the heat reservoir. Similarly, another extension segment is connected between a second riser tube and an output conduit. The heat reservoir is suspended above the fire by the first and second riser tubes. The extension segments allow the depth of the circulator to be adjusted.
The output conduit is connected to the opposite end of the manifold and guides the heated air from the second riser tube back into the manifold. When the heated air exits the output conduit, some of it backs up toward the block in the manifold while the rest is forced through the manifold and discharged into the room to be heated.
It has been discovered that certain aspects of the above mentioned design resulted in the heat exchanger operating inefficiently and that certain parts of the heat exchanger were susceptable to damage due to excess heat. In particular, the funnel shaped conduit between the motor and the manifold restricted air flow therebetween resulting in an inefficient flow volume. Also, with the block located near the center of the manifold, some air would travel past the input conduit to the block where the air would be forced to reverse its direction back toward the input conduit. Once the air returned to the input conduit it flowed into the input conduit. This air flow pattern caused the motor to work harder because of turbulence created near the entrance to the input conduit.
Also, the input and output conduits that connected the manifold with the extension segments restricted the air flow to and from the heat reservoir. This prevented an optimum air flow through the heat circulator and into the room being heated. It also allowed heated air flowing from the heat reservoir to accumulate in the second riser tube thereby becoming very hot resulting in potential damage to the tube leading to potential repair or replacement. Additionally, the separate extension segments between the riser tubes and the input and output conduits each had two joints which contributed to air loss into the fireplace thereby decreasing the heating capacity of the heat exchanger.
Further, it has been discovered that heated air was escaping from the manifold as it rested on the hearth extension. This decreased the efficiency of the heating unit because some of the air was escaping before it could be effectively forced into the room by the blower.
Thus, there still exists a need for fireplace heat exchangers that are relatively inexpensive to manufacture, easily installed within the fireplace, durable efficient, nd compatible with fireplaces that include frame having closable glass doors or wire mesh curtains.